Awareness of podcasting is sitting steady at 45%, up just slightly from last year’s 43%. That’s not the kind of growth that inspires hope that the medium will spread like wildfire. Podcast listening and/or viewing just hasn’t gone mobile – 71% of people who listen to podcasts do so on their desktop and that number has actually increased from last year, according to the study.

So while cell phone usage has soared, podcasting usage has gotten stuck on the desktop, which is one possible explanation for the stagnant growth of the audience. Smartphone streaming has made downloading audio files for listening on mobile phones unnecessary.

It looks like streaming is taking a bite out of podcasting at this point. Online radio’s audience is 70 million monthly (Arbitron/Edison’s Infinite Dial Study).

Podcast consumers tend to be early adopters and social networkers, according to the study. They tend to respond to sponsor ads – 71% said they had visited a website because of an ad they had seen or heard in a podcast.

With wifi and 3G, and soon 4G access more readily available to consumers who want to stream and listen on demand, it’s looking more and more like podcasting is an interim audio technology that has limited long term audience growth because it’s replaceable by audio streaming.

The ability to listen to the content whenever and wherever they want is important to them. These particular consumers also indicate a pretty low frequency of other mainstream media usage. Edison Research’s Tom Webster translates that to mean “A podcast advertising buy is not a redundant media buy for advertisers and marketers. These are attractive, affluent consumers that mass media is losing.”

They own mobile phones that can play audio files, and they listen on their phones. 9 out of 10 podcast consumers prefer advertising within the content to the idea of paying for their content through a subscription fee. However, when asked how they feel about those advertisements, only 2% said they liked them and found them useful. The majority either liked or didn’t like them and occasionally found them useful. They were more positive about sponsorship messages, 72% were either interested in them or didn’t mind them and occasionally found them useful; and 82% reacted that way to sponsorship mentions by program hosts.

A nice majority of podcast consumers indicated that they had taken action after hearing or seeing advertising in audio or video content, with 71% of respondents visiting a web site after hearing a message. Of course, this is not the response rate to any advertising, since these are behaviors that podcast consumers indicate they have ever done, not responses to every ad.

It’s an interesting study that could prove helpful in building value for advertising in podcast platforms. I have begun to wonder about the long term viability of podcasting as a mass appeal platform, as the content that I used to download onto my ipod is now available for on-demand streaming, so I no longer need to subscribe, download and transfer to my portable device. An approach that highlights the podcast population as an appealing group of consumers who are difficult to reach in other ways makes sense, and that’s what this study provides.